The voice coil motor (VCM) is a motor designed according to Lorentz force theory and used for directly switching the electrical signal into the beeline displacement without any intermediate switching mechanism. Compared with other motors, the voice coil motor has a plurality of advantages, such as simple structure, small volume, light weight, low inertia and larger than thrust, etc., so that it has broad application prospects, which is mainly applied to the positioning systems with high precision, high frequency excitation, speediness and high acceleration, optics and measurement systems, optical assembly and aviation.
At present, the design scheme of the servo drive controller of the voice coil motor in the ultra-high precision servo control field is divided into linear power amplifier scheme and PWM (pulse width modulation) power converter scheme. When the ultra-high precision servo system adopts the linear power amplifier scheme to design, the current response is fast, the thrust ripple of the system produced by the on-off chopped wave of the switch is eliminated, and the stability of the output thrust is improved. But when the system adopts the linear power amplifier scheme, firstly the current response has overshoot problem and the nonlinear region while the current leaps. Secondly the design of the controller is greatly limited, and the high performance is difficult to control. When the ultra-high precision servo system adopts the linear power amplifier scheme to design, heat dissipated by the system components is large, and more energy is lost. One of the important development directions of the ultra precision positioning servo system is high overload and high acceleration, undoubtedly the power grade requirement of the element is higher, so that the linear power amplifier scheme is increasingly difficult to meet the power requirements of the ultra-high precision servo control system.
But when the ultra-high precision servo system adopts the PWM power converter scheme to design, because the control signal of the system is controlled by a digital processing unit, the design of the control system of the servo control system of the voice coil motor is more flexible, the drive performance of the system can be controlled by using more complex control methods, at the same time, the system has the advantages of fast response speed and high efficiency. But the PWM power converter scheme has some shortcomings. Firstly because the on-off chopped wave of the switch inevitably produces the current ripple in the system, and then the thrust ripple (the thrust ripple produced by the on-off chopped wave of the switch in the system is generally called thrust ripple below) caused by the current ripple greatly influences the control performance of the servo drive control system of the ultra-high precision voice coil motor. Secondly when the system adopts the PWM power converter scheme, the dead time set for preventing the direct connection of the upper and lower bridge arms of the switch circuit causes the instability phenomenon in the drive system.
At present, to reduce the thrust ripple produced in the system in the PWM power converter scheme, the high switching-frequency drive method is accepted. For example, to reduce the thrust ripple, the designer ascends the switching frequency of the switch to 200 kHz, at the moment, compared with the 10 kHz switching frequency adopted by the drive control system of the traditional servo motor, the thrust ripple of the system is reduced to 5% of original, but at the same time, because the switching frequency of the switch is ascended 20 times from the original, the switching loss of the switch is ascended 20 times from the original, simultaneously because the switching frequency of the switch ascends, the requirements of the switch are improved, and the cost of the drive system is increased. If the switching frequency is ascended, the control difficulty of the control system and the design difficult of the drive circuit of the drive system rise, and the stability of the system is greatly reduced.
In accordance with the former analysis, when the servo control system of the voice coil motor adopts the traditional PWM power converter scheme, the system structure sketch thereof is shown in FIG. 13; because of the on-off chopper wave of the switch of the system, current ripple produces in the main windings, which causes the output thrust ripple of the servo system of the voice coil motor.
The traditional servo adopts the switching frequency below 10 kHz, and the output thrust of the servo drive system of the voice coil motor is shown in FIG. 14A through FIG. 14C.
As shown in FIG. 14A through FIG. 14C, the servo system of the voice coil motor is in the small thrust output state, the range of the output thrust ripple of the system is 9.3398N-3.3324N, the average output thrust is 6.3361N, and the peak value of the output thrust ripple is 6.0074N.
In accordance with the current conventional method for solving the output thrust ripple of the system, when the switching frequency of the drive circuit of the system is increased to 200 kHz, the simulation waveform of the output thrust of the system is shown in FIG. 15A through FIG. 15C.
It is observed that the fluctuation range of the output thrust of the system is 6.9954N-6.6935N when the switching frequency of the drive circuit of the system is increased to 200 kHz, the peak value of the output thrust ripple is 0.3019N, and the output thrust ripple is reduced to 5% of original compared with the 10 kHz switching frequency.